DC regulate T-cell function by promoting either tolerance or activation, and in the latter case, by directing the quality of the ensuing response. New imaging tools now permit direct visualization of the relevant DC-T-cell interactions in vivo and have provided a new perspective on the dynamics of these crucial cellular contacts. In this Viewpoint, we discuss the insights generated by direct visualization of DC-T-cell interactions and the controversies/unanswered questions that need to be addressed in future work.